1. Field of the Invention
This invention is related to vacuum insulation panels and more particularly to apparatus for selectively enabling and disabling, i.e., turning "on" and "off," the thermal insulating effect of compact vacuum insulation panels.
2. Description of the State of the Art
In our co-pending patent applications, Ser. No. 07/856,840 (now U.S. Pat. No. 5,175,975) and Ser. No. 07/535,782 (now U.S. Pat. No. 5,157,893), we described the need for better, more compact, and more versatile insulation products. The principal invention described in those patent applications provided a significant advancement in compact vacuum insulation that is thin, bendable, very effective insulation. That principal invention also provided compact vacuum insulation that has a very long useful life, yet has interior and exterior structures that are easy to manufacture. Such compact vacuum insulation is very effective for applications where the need for thermal insulation is constant and where static insulation can meet such a need. However, there are many applications that can benefit greatly by a changeable insulation that can be selectively enabled and disabled, i.e., turned "on" and "off," at desired times. For example, in applications where it is desired to retain heat for some period of time and then to dissipate heat for another period of time, it would be helpful to have insulation that can be turned "on" and "off."
There have been some apparatus and methods developed for enabling and disabling insulation. For example, U.S. Pat. No. 3,450,196 to P. Bauer discloses the general concept of enabling and disabling vacuum insulation panels by varying or controlling the gas pressure (vacuum) within the panels. The T. Xenophou patent, U.S. Pat. No. 3,968,831 applied that principle to building walls by connecting partial vacuums in the walls to a vacuum pump.
H. Bovenkerk, in his U.S. Pat. No. 3,167,159, disclosed the rather clever idea of using a metal hydride in combination with a small heating element, to selectively enable and disable vacuum insulation. The hydride naturally absorbs and retains hydrogen, and it can be heated to release the hydrogen into the vacuum insulation in large enough quantities to disable the vacuum insulation. Upon cooling, the hydride reabsorbs the hydrogen gas to again enable the vacuum insulation. Gross et al. used metal hydride and a heating element to heat the hydride for disabling and enabling vacuum insulation around a sodium-sulphur battery in his U.S. Pat. No. 4,235,956. While such Bovenkcrk and Gross et al. devices can work for enabling and disabling vacuum insulation, they have the disadvantage of having to keep the heating element powered for as long as the insulation is to be disabled, i.e., for as long as good heat transfer is needed. In some applications, where power availability is limited and needs to be conserved, such a constant power drain can be very inconvenient, if not intolerable.
H. Buchner, in his U.S. Pat. No. 4,224,980, used the hydride hydrogen storage and release concept in a passive sense for essentially self-regulating heat retention and dissipation with vacuum insulation around a fuel injection/ignition chamber in a diesel engine. He uses the vacuum insulation to retain heat in the injection/ignition chamber as the diesel engine warms up, but he then relies on heat from the injection/ignition chamber itself to heat the hydride and release hydrogen to disable the vacuum insulation as the temperature of the diesel engine around the injection/ignition chamber rises. D. Dechert accomplished a similar result with the self-regulating vacuum insulation disclosed in his U.S. Pat. No. 3,424,622, to maintain the 300.degree. C. operating temperature of a fused salt battery, although he used a solid or liquid with vapor pressure that increases with temperature, instead of a metal hydride and hydrogen, to vary the insulating effectiveness of the vacuum insulation. These Buchner and Dechert devices are effective for passive enabling and disabling of vacuum insulation at inherent temperatures according to the materials and systems designs, but they are not capable of individual control, or of being turned "on" and "off" at arbitrary or different temperatures.